PTL 1 shows the structure of an air flow rate measuring device. In the air flow rate measuring device, a sensing element for measuring a physical quantity is provided on a circuit substrate on which a circuit portion is formed. The circuit portion of the circuit substrate is disposed in a case. The sensing element of the circuit substrate is exposed into a bypass passage. In PTL 1, the sensing element of the circuit substrate is electrically joined by a metal wire, and a joined portion is sealed with a synthetic resin material.